audiopolicy: Primary Output runtime management

In case of unavailability of device(s) attached to the primary output,
this output can be disconnected.
The cache variable must be resetted, then restored when at least one
device supported by one profile of the primary output is made
available again.

Test: adb shell /data/nativetest64/AudioPolicyEmulatorTests/AudioPolicyEmulatorTests --gtest_filter=AudioSourceTest*

Signed-off-by: Francois Gaffie <francois.gaffie@renault.com>
Change-Id: Iae8937cad3d70b0e8c7ff4516c27aa8eff231eaa